1. Field of the Invention
This invention relates in general to electronic devices, and more specifically to the use of semiconductor materials to fabricate thermionic coolers and generators.
2. Description of Related Art
The use of electronics to transport heat to and away from certain areas has expanded in recent years due to increased packing densities and hostile environments. For cooling applications, thermoelectric (TE) coolers have been used to cool areas both in electronic and nonelectronic applications. TE coolers typically include a p-type doped region alternatively connected to an n-type doped region, which creates cooling effects at one metal-doped region junction and heating effects at the other metal-doped region junction, depending on the direction of the current through the device.
However, TE coolers are limited in their overall efficiency by the bulk properties of the materials used in the TE cooler. Further, the reliability of assemblies of many elements, such as in TE coolers, is often not sufficient for many applications. The cost of TE coolers has not dropped at the same rate as other electronic devices such as transistor circuits, lasers and detectors, because TE cooler elements are not fabricated using high volume planar integrated circuit technology. Further, TE coolers that can generate a large cooling effect tend to be large devices, typically 1 cmxc3x971 cm or larger, and are slow cooling devices, and thus, are not acceptable in small electronic devices.
From the foregoing, it can be seen then that there is a need for improved electronic coolers. It can also be seen then that there is a need for better electronic cooler fabrication techniques. It can also be seen that there is a need for low cost electronic coolers. It can also be seen that there is a need for more space efficient electronic coolers. It can also be seen that there is a need for more energy efficient electronic coolers. It can also be seen that there is a need for coolers with faster response times. It can also be seen that there is a need for more reliable electronic coolers. It can also be seen that there is a need for electronic coolers that reach lower temperatures.
The present invention minimizes the above-described problems by using bandgap engineering and modulation doping to fabricate small thermionic coolers that operate at room temperature. By using proper materials and geometries, efficient and space conserving thermionic cooler elements which can reach lower temperatures are fabricated in a cost-effective manner. Further, these coolers can have a much faster response.
The present invention comprises a method and apparatus for theomionic cooling. The method of the present invention comprises growing two semiconductor layers. The second layer has a variable conduction bandedge as a function of distance (for the case of electron transport) which has a Fermi level on the order of kBT from the bandedge of the semiconductor layer. This structure allows for selective thermionic emission of high energy carriers from cathode to anode that suppresses the reverse current, and creates a cold junction at the cathode and a hot junction at the anode. Using the same device in contact with a hot and a cold bath will create a thermionic generator.
One object of the present invention is to provide better electronic cooler fabrication techniques. It is a further object of the invention to reduce electronic cooler fabrication costs. It is a further object of the invention to make more efficient electronic coolers which reach lower temperatures. It is a further object of the invention to make electronic coolers that have a faster response time.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.